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| faq_slow 2021-10-11 | faq_slow 2025-05-13 06:50 (current) | ||
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| In case the speed is throttled by %%CPU%%, it may help if you choose different encryption algorithm on //[[ui_login_ssh#encryption_options|SSH page]]// of Advanced Site Settings dialog (supposing you are using SSH-based [[protocols|file transfer protocol]], such as SFTP or SCP). //Blowfish// is usually a lot faster than //AES//. It may also help, if you turn off [[ui_login_ssh#protocol_options|compression]], if you have turned it on before. | In case the speed is throttled by %%CPU%%, it may help if you choose different encryption algorithm on //[[ui_login_ssh#encryption_options|SSH page]]// of Advanced Site Settings dialog (supposing you are using SSH-based [[protocols|file transfer protocol]], such as SFTP or SCP). //Blowfish// is usually a lot faster than //AES//. It may also help, if you turn off [[ui_login_ssh#protocol_options|compression]], if you have turned it on before. | ||
| - | porn | + | ===== Network Delay/Latency ===== |
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| + | Network delay/latency affects particularly %%SFTP%%, as it is a packet oriented-protocol. When transferring, the SFTP client (WinSCP) sends a read/write request to the SFTP server, waits for a response; and repeats, until the end of the file. | ||
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| + | Even if your connection is fast, if the server is far away (or slow), it takes a time for the response to arrive back. If the client spends this time uselessly waiting, your transfer speed will be low. | ||
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| + | Most SFTP clients (including WinSCP) overcome the problem by both requesting/sending a large chunk of the file in each single read/write request and by sending (queuing) multiple requests without waiting for a response to previous. For example WinSCP can request up to 32 chunks for 32 KB each at once, totaling 1 MB (these are defaults which can be altered with ''SFTPDownloadQueue'' and ''SFTPUploadQueue'' [[rawsettings|raw session settings]]). But if there's a big discrepancy between the bandwidth and the network delay, even that 1 MB can be too small to saturate the bandwidth. | ||
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| + | See also [[wp>Bandwidth-delay_product|Bandwidth-delay product]] on Wikipedia. | ||
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| + | In case the speed is throttled by a connection latency, it may help if you use [[scp|SCP protocol]] instead of [[sftp|SFTP]]. %%SCP%% is less affected by the latency. Though we got reports of exactly opposite behavior too (SFTP being faster than SCP). When connection latency is the bottleneck, it may additionally help if you turn on [[ui_login_ssh#protocol_options|compression]] (though that will have small effect if you are transferring large media files, which are compressed already). Toggling //[[ui_login_connection|Optimize connection buffer size]]//, in either way, can help too. | ||
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| + | An underlying TCP protocol can suffer a similar problem too. In which case it will affect all other protocols, including SCP, FTP, WebDAV or S3. | ||
| ===== Relation to PuTTY PSCP/PSFTP ===== | ===== Relation to PuTTY PSCP/PSFTP ===== | ||
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| If WinSCP started being slow suddenly, check if you did not [[ui_pref_logging|enable logging on //"Debug"// level]] inadvertently. | If WinSCP started being slow suddenly, check if you did not [[ui_pref_logging|enable logging on //"Debug"// level]] inadvertently. | ||
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| + | ===== [[transfer_queue]] Parallel Transfers ===== | ||
| + | When comparing batch file transfer speed of WinSCP, note that it by default transfers all files sequentially using a single connection. While some other clients use multiple connection by default. If you prefer, you can [[transfer_queue|transfer files using multiple parallel connections]] in WinSCP too. | ||